Polycarbonate compositions have been employed for various applications meeting minimal requirements for flame retardancy and/or for having minimal requirements for transparency. Examples of such polycarbonate compositions are described in EP1288262B1 (e.g., describing a broad range of silicone compounds, such as silicone compounds having a degree of polymerization greater than 9 in paragraphs 0191 and 0192, for achieving a minimal level of flame retardancy), EP2121826B1 (e.g., describing composition flame retardant compositions including PTFE, a silsesquioxane, and a charring salt flame retardant), and EP2058369B1 (e.g., describing a broad range of light diffusing technologies and the use of branched silicones for flame retardancy), all incorporated herein by reference in their entirety.
Although EP1288262 B1 describes compositions that meet a portion of the UL-94 V-0 test at 1.5 mm (i.e., the dripping performance after only the first two applications of flame ignition), there is no description of composition meeting the entirety of the UL-94 V-0 test at 1.5 mm. Additionally, EP1288262 B1 does not describe compositions meeting the more demanding test of UL-94 V-0 at 1.0 mm.
Thus, there is a need for materials having improved flame retardancy and improved optical properties for applications where these characteristics are important, such as lighting. For example, there is a need for polycarbonate compositions for use in housings to protect or otherwise shroud the light source (e.g. LED, incandescent bulb, florescent bulb, etc.) and/or to diffuse the light from the light source. For manufacturers to economically produce the housing (e.g., shrouds), there is also a need for polycarbonate compositions having excellent processability characteristics to allow the composition to be formed (e.g., by extruding, injection molding, or blow molding, etc.) into desired shapes.
For example, there continues to exist a need for a highly transparent flame retardant polycarbonate compositions having a high level of transparency (e.g., having a high total luminous transmittance and/or a low haze) and good flame retardancy (e.g., achieving the requirements for one or more of the following UL-94 standards: V-0 at 1.0 mm, 5VB at 2.5 mm, or 5VA at 2.5 mm). For example, there is a need for polycarbonate compositions having a high total luminous transmittance, a low haze, and meeting all of the following UL-94 standards for flame retardancy: V-0 at 1.0 mm, 5VB at 2.5 mm and 5VA at 2.5 mm. In particular, there is a need in lighting applications for polycarbonate compositions having a total luminous transmittance of about 90.0% or more, and a haze of about 1.0% or less (e.g., at a thickness of 1.0 mm).
There is also a continuing need for a light diffusing flame retardant polycarbonate composition having a high level of haze and good flame retardancy (e.g., achieving the requirements for one or more of the following UL-94 standards: V-0 at 1.0 mm, 5VB at 2.5 mm, or 5VA at 2.5 mm). For example, there is a need for polycarbonate compositions having a high total luminous transmittance, high haze, and meeting all of the following UL-94 standards for flame retardancy: V-0 at 1.0 mm, 5VB at 2.5 mm and 5VA at 2.5 mm. In particular, for light diffusing lighting applications, it is desired to have a total luminous transmittance of about 50% or more and a haze of about 50% or more, preferably about 70% or more, and most preferably about 80% or more (at a thickness of 1.0 mm).
Although the previously cited references teach compositions which may have some level of flame retardancy and/or some level of light transmittance/haze, there is no teaching or suggestion for the demanding properties achieved according to the teachings herein, or how one may select from the multitude of ingredients, concentrations, and combinations to achieve these properties.
Prior attempts to achieve polycarbonate formulations that are light diffusing have not achieved the level of flame retardancy, processability, high light transmittance, and high haze required in various applications. For example many diffusing agents negatively impact the flame retardancy of polycarbonate compositions, negatively impact the processability of the composition, or both.